Method of making bleach liquor as by-product in salt purification



LSBASL Sei., 4, i928.

V, YNGVE METHOD OF MAKING BLEAGH LIQUOR AS BY-PRODUCT INSALT PURIFICATION original Filed Aprgl 9, 1925 MMF@ mm E im im Patented Sept. 4, 1928.

UNITED STATES PATENT O/FFICE'.l

VICTOR YNGVE, OF LAKEWOOD, OHIO.

METHOD OF MAKING BLEACH- LIQUQR AS BIZ-PRODUCT IN SALT PURIFIGATION.

Original application filed April 9, 1925,

The present invention relates to new and useful improvements in methods of purifying salt and of recovering and utilizingcertain ley-products.

This -application'is a division of iny copending application #21,844, filed Apr1l 9, 1925. v

The process will be described as a complete cycle, though it will be obvious to those skilled in the art that certain processes have a much wider application and may be used entirely apart from other processes. This inyention utilizes some of the principles described in my Patent No. 1,520,920-a'nd is in part an extension of that invention.

The starting point of the process involved in the present invention is brine, which may be of any suitable concentration but preferably contains about 300 grams of sodium chloride per liter. The brine may be natural or vartifclal, made from any available commercial grade of salt and may be subjected to pretreatment. A typical brine which may be used, though it is v not to be considered 1n a limiting sense, is the following:

Grams per liter.

Sulphur Trioxide 3. 'The process is best explained by means of the attached drawing, though it is understood that variations in the procedure will occur to those skilled in the art without departing from the spirit of the invention.

The crude brine is treated in container I with sodium hydroxide. The Sodium hydroxide can be added in any suitable manner, but preferably the main portion of it is added just as it 'cornes from XVI, caustic-.chlorine cells, and salt is also. present in the caustic solution. Sodium hydroxide is also added from other parts of the process as will be disclosed later. The sodium hydroxide is added in excess of the amount to precipitate the magnesium kand calcium present in .the brine. The amount may vary from a fraction of one er cent to ve per cent or more, but referably about 10 grams per liter, is adde The mixture is preferably heated to about 100 C. and the sludge ofhydroxides is filteredoff or allowed to settle in II. The clear brine is`- Serial No. 21,844. Divided and this application filed January 12, 1927. Serial No. 160,648. p A

vstored in III from which it goes to evapora tors IV, V and VI.

' In the evaporators the brine is concentrated and salt separates out. Sodiumhydroxide and sodium sulphate become concentrated in the mother liquor. When thesodium hydroxide concentration reaches a suitable percentage, which may be for instance, from one to ten per cent, part of the mother liquor may be withdrawn from the evaporators and added as indicated, to I, where it puries more brine. The exact percentage ofthe NaOH in the mother liquor may be varied to suit operating conditions. Meanwhile, the sodium sulphate becomes more concentrated and is removed in a manner to be hereinafter set forth. The purified salt and adhering mother liquor passes to f centrifuge VII, where the mother liquor is separated and the salt is washed either with puridicated from hydrogen and chlorine from the chlorine-caustic cells XVI. This neutral brine may, if preferred be used in the eva-porators IV, Valid as indicated.' The Washing solution may go backto the evaporators.

When the sodium sul hate concentration vhas become sufficiently igh in the mother liquor it is removed by the following procedure: mother liquor is taken` from the evaporators and stored in XIV where it is cooled to about 20 C. This separates out some sodium chloride. The clear solution then passes throughv the precooling coil or tank XXII and to the tank or coil XXIII, where the solution is finally refrigerated to a temperature suitable for separating out the hydrated sodium sulphate. A temperature of about 0 C. is preferred though higher or lower temperatures may be used. The percentage lof sodium sulphate deca-hydrate which separates out depends on the percentage of sodium hydroxidev 'in the brine. With a brine carrying 3% NaCl-I 6% to 9% of the de cahydrate may be recovered. With the NaOH concentration higher less sodium sulphate is held in the brine and with the concentration lower, more is held in the brine. The refrigerating systems XXII and XXIII may be provided with suitable stirrers and Scrapers to keep the crystals from adhering to the sides of the, systems. I have-'found that these solutions tend readily to supersaturate with rrespect to sodium sulphate and I prefer to alcated. The wash water may go back, as in-A cated to IX.

The brine from XIV may also go to XII where itis treated with a solution of sodium hydroxide obtained from the cells XVI through XIII and XXIV, which separates out sodium sulphate either hydrated or anhydrous, depending on the temperature and composition of the solution in which it is prey cipitated. The sodium sulphate is separated by the centrifuge X and the mother liquor,

containing an excess of sodium hydroxide,

` goes back to I to purify more brine.

The mixture of calcium hydroxide, magnesium hydroxide and other hydroxides in XVII is treated with chlorine, preferably'direct from the cells XVI, either before. the

sludge is washed or after washing. This sludge will usually contain comparatively large amounts of magnesium hydroxide. Such percentages may be 10 to 20% or even higher.' I have found that han excellent bleach liquor can be made from this sludge if the chlorination is stopped before the magnesium hydroxide is chlorinated. If the chlorination'is carried too far, large percentages of chlorates are formed. It has always beenv considered that large percentages of magnesium hydroxide in a bleach sludge rendered the sludge useless for bleach liquor, but I have discovered that it need not be detrimental if the chlorination is not carried too far. The magnesium hydroxide remaining may be converted into various magnesium comn pounds or mixtures.

` The present method of obtaining sodium sulphate may be used in conjunction With any other salt manufacturing process in which calcium is removed from the brine which, in the present case, occurs when the brine is treated with sodium hydroxide.

What I claim is:

1. The process of obtaining bleach liquor as a byproduct in the purification of salt which comprises mixing with a brine containing magnesium and calcium an amount of sodium hydroxide in excess of the amount necessary to precipitate the magnesium and calcium, heating the mixture to about 10() degrees, separating the precipitated hydroxide sludge and chlorinating the said sludge only to the extent that no appreciable amount of magnesium hydroxide is chlorinated.

Y2. The process of obtaining a bleaching solution which consists in chlorinating a mixture of magnesium and calcium hydroxides and stopping the chlorination before any appreciable amount of magnesium hydroxide is chlorinated.'

3. The process of obtaining bleach liquor which consists in treating a brine containing calcium or magnesium or both with sodium hydroxide, separating the precipitated hy- -droxides and chlorinating the mixture only to the extent that no appreciable amount of magnesiumhydroxide is chlorinated.

In testimony whereof, I have signed my name to this specification, this 30th day of December, 1926. VICTOR YN GVE. 

